Security readout for executives and security teams
Plain-English summary
Cisco NX-OS devices can be forced into a denial-of-service condition when they mishandle certain IPv6 traffic sent to the device. The issue can exhaust network-stack buffers and disrupt management or control-plane operations. Restoring normal operation may require manual intervention.
Executive priority
Prioritize if Cisco NX-OS devices support critical routing, switching, or data-center operations and are reachable over IPv6. Treat as a high-availability risk, especially where management or control-plane disruption would affect business services.
Technical view
CVE-2021-1387 is a CWE-401 resource-release flaw in the Cisco NX-OS network stack. An unauthenticated remote attacker can trigger buffer exhaustion with certain IPv6 packets destined to an affected device, impairing control-plane and management-plane protocols. CVSS 3.1 score is 8.6.
Likely exposure
Exposure is most likely in environments running Cisco NX-OS Software where IPv6 traffic can reach affected device interfaces. The provided bundle does not list exact affected versions, platforms, or fixed releases.
Exploitation context
The source bundle does not report active exploitation, and KEV status is false. Risk is still material because the attack is network-reachable, requires no authentication, and can affect availability of critical network infrastructure.
Researcher notes
The bundle identifies Cisco NX-OS Software broadly but does not include exact version data. Analysis should start from Cisco's advisory. Avoid assuming exploit-in-the-wild activity without KEV or another cited source.
Mitigation direction
- Review Cisco's advisory for affected NX-OS releases and vendor-recommended fixes.
- Apply Cisco-recommended software updates or mitigations where applicable.
- Restrict IPv6 reachability to device management and control-plane interfaces where operationally feasible.
- Monitor affected devices for buffer exhaustion or management/control-plane impairment.
- Plan manual recovery procedures for impacted devices.
Validation and detection
- Inventory Cisco NX-OS devices and current software releases.
- Check whether IPv6 traffic can reach device interfaces.
- Compare installed releases against Cisco's advisory.
- Review monitoring for management or control-plane protocol impairment.
- Confirm operational runbooks cover manual restoration after DoS.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-401: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2021-1387 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 8.6 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H3.94Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
8.6HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
Source materials
- CVE List V5 sourceCVE List V5
- 20210224 Cisco NX-OS Software IPv6 Netstack Denial of Service VulnerabilityCVE reference · vendor-advisory, x_refsource_CISCO
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Missing Release of Memory after Effective Lifetime
Missing Release of Memory after Effective Lifetime represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.